At one time, large windows, glass doors and the like had to be made up of multiple small glass panes, held in place by structural grids called muntin bars. Now that windows can be formed less expensively, for example, from a single large glass sheet, muntin bars are used as decorative features to simulate classic multiple pane windows. Although muntin bars are sometimes commonly referred to as colonial bars, georgian bars or grill bars, I will refer to these decorative features as muntin bars. Also, although these decorative muntin bars are useful in windows, doors and the like, I will refer to their use in windows, for ease of discussion.
A decorative muntin bar grid is generally attached to a frame or spacer at the perimeter of the window and can be either mounted between parallel panes of glass in a window, as in an insulative glass (IG) unit, or on the inside or outside surface of the window.
Decorative muntin bars are generally constructed from aluminum, another suitable metal, or a suitable plastic. In the case of aluminum or other metal, the muntin bars are commonly roll-formed by a continuous process in which a flat strip is rolled into an elongated hollow bar, creating a seam where the ends of the flat strip are brought together. Individual muntin bars are then cut from this elongated bar. Muntin bars can also be extruded or, particularly in the case of plastic, pultruded. Pultrusion is similar to extrusion, except that the material in pultrusion is drawn, rather than pushed, through a die. Regardless of the formation process, muntin bars are typically hollow, with a uniform (often flat rectangular) cross section.
A muntin bar grid is typically assembled in one of two ways. In one arrangement, a joining element is provided at each intersection of the grid. A number of short muntin bar segments are joined together at their ends by each of these joining elements. Each joining element has a number of extensions which are friction fit into the ends of the segments. U.S. Pat. No. 4,723,388, entitled "Easily Formable Grid for Windows and the Like", to Zieg, illustrates an example of such a structure.
In the other common arrangement, longer bar segments are overlapped to form the grid. Overlapping bars are provided with complementary notches so that the bars can interfit at each intersection into a relatively flat unit. Concealed joiners sit within the notches at each intersection and extend into each of the overlapped bars to hold the bars together. U.S. Pat. No. 4,060,950, entitled "Concealed Clip for Hollow Strips", to Rackard et al., shows an example of such a muntin bar assembly.
Muntin bars are generally joined to a frame or spacer by using end-pins which fit into corresponding holes in the spacer. The end-pins are typically provided in an assembly which is friction fit into the end of each muntin bar. A flange on the assembly abuts the end of each muntin bar to prevent the assembly from being forced too deeply into the muntin bar.
Traditional muntin bars, particularly those of the overlapping assembly type, suffer from several structural and aesthetic drawbacks. The notches at the intersection points are generally formed by a notching jig or punch which stamps out each notch after the bar has been formed, often damaging the material surrounding the notch. The muntin bars, especially those that are notched, are also prone to bending during preinstallation handling. Further, the concealed joiners used with notched bars are difficult to handle, making the joining process labor intensive and increasing the likelihood of damaging the bar. If the muntin bars are too flimsy and are deflected during or after installation, they can damage any interior coating of the glass. In the case of a roll-formed muntin bar, friction fitting the end-pin assembly into the end of the bar often forces the seam open, which is unsightly and detrimental to the structural integrity of the assembly. This can also be true of the joining elements used in non-overlapping grid arrangements. In addition, the flange of the end-pin assembly will often be visible at the end of the muntin bar, undermining the aesthetic effect.
Most of the above-noted structural problems can be addressed by forming the muntin bar from sufficiently thick or sturdy stock material. However, using thicker material is not only more expensive and less attractive, but also to some extent undermines the insulative properties of an IG unit. To a degree, the thicker the material of the muntin bar is, a greater conduit is provided for heat transfer, and the poorer the thermal insulation provided by the window.
The seam of the roll-formed bar can also be prevented from spreading by welding, which also provides some structural rigidity to the overall bar. However, welding the seam adds another production step, further increasing production costs. Welding also presents aesthetic problems. In order to avoid an unsightly welded seam, the welding must be done internally or the seam must be treated after welding, either of which adds to the cost of production.
Attempts have been made to reinforce hollow bar or beam structures, none of which is wholly satisfactory for use with muntin bars. For example, U.S. Pat. No. 5,285,612, entitled "Interlocking Joint with Notch Reinforcement", to Johnson, relates to notched beams which interlock to form a rigid joint without fasteners. Insert bodies, with notches conforming to the notches in the beams, are inserted into the beams to reinforce the notched areas. However, these inserts do not reinforce the beams during the notching process, nor do they reinforce the portions of the beams remote from the notches.
U.S. Pat. No. 4,580,380, entitled "Composite Filled Interior Structural Box Beams", to Ballard, relates to a composite structural beam with two duplicate flange members and two duplicate web members interconnected in a box form. A lightweight, space-filling bulk substance, such as a foamed plastic, fills the structural beam. While well suited for structural beams, this arrangement is too complex and expensive to be used in a muntin bar assembly.
Foam filling, such as that discussed in the Ballard patent, has been employed in roll-formed products in other industries. For example, roll-up storm shutters have been roll-formed and foam-filled, as described in an article entitled "New Roll Forming Line Fulfills 15 Year Dream of Quality", by Harvey J. Arbuckle, appearing at page 29 of the July 1995 issue of Metal Forming and which is incorporated herein by reference. However, foam filling has not been applied to muntin bar assemblies.
Thus, there is a need in the art for a decorative muntin bar for windows and the like which is reinforced during notching to prevent collateral damage. There is a further need for a muntin bar with a reinforced seam and/or an end-pin assembly which does not impart as much seam-spreading force as traditional end-pin assemblies. Further, there is a need in the art for a mechanism to reinforce the muntin bar, especially the notched portion thereof, during preinstallation handling. There is also a need to reinforce the overall bar so that the bar material and the bar itself can be made thinner. There is a further need to facilitate the joining or interconnection (hereinafter "joinder") of muntin bars to one another and to a peripheral frame. There is an additional need for a muntin bar in which an end-pin can be seated within the muntin bar, improving the overall aesthetic appearance of the bar.